Wood laminate and method of making

ABSTRACT

A method of making a fiber glass mat especially useful for bonding to wood contains glass fibers and a “B” staged resin is disclosed. A substantial portion of the resin binder can be a furfuryl alcohol formaldehyde, phenol formaldehyde, melamine formaldehyde, or any other resin that can be “B” staged. Also, a method of making wood and wood product laminates using this new mat without any other adhesives, and the resultant laminates are disclosed.

This application is a division of U.S. application Ser. No. 08/728,655,filed Oct. 10, 1996 now U.S. Pat. No. 5,837,620 issued on Nov. 11, 1998.

The present invention involves a method of making mats having particularuse in bonding to wood and in making improved wood products and themethod of making such mats. The mats produced according to thisinvention are useful as reinforcement and dimensional stabilizers formaking a large number of novel laminate products such as wood laminatesof all types, hard faced wood products such as plywood and hardboard formaking concrete forms and many other similar uses. The mats are alsouseful as stabilizing and reinforcing substrates for various otherproducts. The invention also includes the method of making the laminatesand the resulting laminates.

BACKGROUND

It is known to make reinforcing mats from glass fibers and to use thesemats as substrates in the manufacture of a large number of roofingproducts. Any known method of making nonwoven mats can be used, such asthe conventional wet laid processes described in U.S. Pat. Nos.4,112,174, 4,681,802 and 4,810,576, the disclosures of which areincorporated herein by reference. In these processes a slurry of glassfiber is made by adding glass fiber to a typical white water in a pulperto disperse the fiber in the white water forming a slurry having a fiberconcentration of about 0.2-1.0 weight %, metering the slurry into a flowof white water to dilute the fiber concentration to 0.1 or below, anddepositing this mixture on to a moving screen forming wire to dewaterand form a wet nonwoven fibrous mat.

This wet nonwoven mat of glass fiber is then transferred to a secondmoving screen and run through a binder application saturating stationwhere an aqueous binder mixture, such as an aqueous urea formaldehyde(UF) resin based binder mixture, is applied to the mat in any one ofseveral known ways. The binder saturated mat is then run over a suctionsection while still on the moving screen to remove excess binder. Thewet mat is then transferred to a wire mesh moving belt and run throughan oven to dry the wet mat and to cure (polymerize) the UF based resinbinder which bonds the fibers together in the mat. Preferably, theaqueous binder solution is applied using a curtain coater or a dip andsqueeze applicator, but other methods of application such as sprayingwill also work.

In the drying and curing oven the mat is subjected to temperatures up to450 or 500 degrees F. for periods usually not exceeding 1-2 minutes andas little as a few seconds. Alternative forming methods include the useof well known processes of cylinder forming, continuous strand matforming which lays continuous strands of glass fibers in overlappingswirls, and “dry laying” using carding or random fiber distribution.

UF resins, usually modified with one or more of acrylic, styrenebutadiene, or vinyl acetate resins, are most commonly used as a binderfor fiber glass mats because of their suitability for the applicationsand their relatively low cost. Melamine formaldehyde resins aresometimes used for higher temperature and/or chemical resistantapplications. To improve the toughness of the mats, a combination ofhigher mat tear strength and mat flexibility, which is needed to permithigher processing speeds on roofing product manufacturing lines and formaximum roofing product performance on the roofs and in otherapplications, it is common to modify or plasticize the UF resins asdescribed above.

Mats made in the above described manner perform well in manyapplications, but do not provide the bonding strength desired forbonding to wood products.

SUMMARY OF THE INVENTION

In the conventional processes of making a nonwoven fiber mat by theprocesses described above, a slurry of fiber, preferably glass fiber, ismetered into a stream of whitewater, preferably cationic to nonionic,and formed into a wet nonwoven mat on a moving, permeable surface andthe mat is thereafter bonded with an aqueous urea formaldehyde (UF)binder, preferably an aqueous UF binder in water and modified by mixingin polyvinyl acetate and/or acrylic tripolymer, dried and cured. Thepresent invention uses this general process to make mats, but includesthe improvement of using a different binder resin, an aqueous furfurylalcohol formaldehyde, phenol formaldehyde, melamine formaldehyde,mixtures of these resins in aqueous solution and other similar resins,to produce mats in which the resin binder is dried and “B” staged, i. e.only partially cured. In a “B” staged condition the resin binderprovides adequate strength to handle and further process the mat, butretains the ability to bond to wood and to “flow” (plastic deformation)under heat and pressure prior to finally curing, much like athermoplastic resin, permitting densification of the fiber glass matwithout damaging the fibers before becoming fully cured, i. e.thermoset.

The mats of the present invention comprise glass fibers bonded togetherwith a resin binder wherein the resin binder is only partially cured toa “B” stage condition. The mats of the present invention have lowerphysical properties initially like tensile strength, hot wet strengthand tear strength than conventionally cured mats, but the mats of thepresent invention surprisingly produce substantially higher bondingstrength with wood.

These mats are then used in the manufacture of wood products wherein oneor more layers of the inventive mat are bonded to one or more layers ofwood or a wood product like particle board, chip board, oriented strandboard, plywood, hardboard, etc., and the resulting laminate are thensubjected to high pressure and sufficient heat to finish curing the “B”staged resin in the mat, and any additional resin that might be used tobond the mat to the wood. Wood products and laminates made using themats of the present invention are a part of the present invention andhave surprisingly good rigidity and strengths, and when the inventivemats are bonded to the surface of wood or a wood product, the resultantwood product has a surprisingly tough surface. The “B” staged resin inthe mat must be compatible with the thermosetting laminating glues usedin the wood composite industry, including urea formaldehyde, phenolformaldehyde, melamine formaldehyde and hot melts.

The mats of the present invention can also contain pigments, dyes, flameretardants, and other additives so long as they do not significantlyreduce the ability of the mat to bond to a wood surface. The pigments orother additives can be included in the fiber slurry, the binder slurryor can be sprayed or otherwise coated onto the mat later using knowntechniques.

DETAILED DESCRIPTION OF THE INVENTION

Mats of the present invention contain about 25-75 weight percent fibersand about 15-75 percent binder. The majority of the fibers are glassfibers. The glass fibers which can be used to make mats can have variousfiber diameters and lengths dependent on the strength and otherproperties desired in the mat as is well known. It is preferred that themajority of the glass fibers have diameters in the range of less than 1up to 23 microns or higher, with the major portion of the fiber beingpreferably in the range of about 6 to 19 microns and most preferably inthe range of about 8 to 16 microns. Up to 50 percent of the glass fibersin the mat, on a weight basis can be microfiber, i. e. fiber havingaverage diameters below 1 micron but, including fiber having averagediameters up to 3 microns. The glass fibers can be E glass, C glass, Tglass, S glass or any known glass fiber of good strength and durabilityin the presence of moisture. Normally the glass fibers used all haveabout the same target length, such as 0.25, 0.5, 0.75, 1 or 1.25 inch,but fibers of different lengths and different average diameters can alsobe used to get different characteristics in a known manner. Microfibers,by their nature, will usually have random lengths under 0.25 inch.Fibers up to about 3 inches in length can be used in a wet process formaking fiber glass mats and even longer fibers can be used in some dryprocesses. Generally the longer the fiber, the higher the tensile andtear strengths of the mat, but the poorer the fiber dispersion.

While the majority of the fibers used in the present invention are glassfibers, a minor portion of non-glass fibers can also be used, such ascellulosic fibers including wood pulp of all kinds, cotton linters,cellulose derivatives such as cellulose triacetate, rayon, etc. Man madeorganic fibers such as Nylon™, polyester, polyethylene, polypropylene,etc. can also be used instead of cellulose fibers in any various blendswith one or more cellulosic fibers. As will be seen later, it isparticularly advantageous to have a higher concentration of cellulosicfibers on one or both surface portions of the mat, extending into themat thickness a small distance, with a higher concentration of glassfibers in the center portion of the mat to enhance bonding of the mat towood.

The binders used to bond the fibers together are resins that can be putinto aqueous solution or emulsion latex, that can be “B” staged, andthat bond good to wood. Typical resin based binders meeting thisdescription are furfuryl formaldehyde, phenol formaldehyde resole andmelamine formaldehyde and other similar resins. Of these, furfurylformaldehyde resin is much preferred because of its bonding power towood, its ease to “B” stage cure, its reduced levels of volatile organiccompound (VOC) emissions, its zero phenol content and its stability instorage. Furan resins of the type useful in this invention are describedin U.S. Pat. No. 5,545,825, the disclosure of which is herebyincorporated herein by reference.

A particularly useful furfuryl alcohol formaldehyde resin for use inthis invention is a FAREZ® resin, such as XP4, available from GreatLakes Chemical Corporation of West Lafayette, Ind. This resin is afurfuryl alcohol based, highly reactive, water compatible resincontaining low levels of volatile components. It has a specific gravityof 1.24 grams/cc, contains 17-21 percent water, has a viscosity of800-1200 cps., a maximum furfuryl alcohol content of about 1 percent, amaximum free formaldehyde content of about 4 percent and a pH of 4-5.This resin contains only about 2 percent non furfuryl alcohol componentswhich are typically about 0.05 percent water, about 0.3-0.7 percentfurfural, and about 0.5 percent 2-methyl furfuryl alcohol. this resin isfully compatible with numerous phenolic, urea and melamine resin basedbinders.

A particularly useful phenol formaldehyde resin for use in the presentinvention is GP 144D64, a plasticized phenolic resin available fromGeorgia Pacific. Another resin useful is a methylated, low formaldehydemelamine formaldehyde resin like Astromel® CR-1 available from AstroIndustries, a division of Borden, Inc.

When these resins are used conventionally as a binder it is normal toadd a strong acid catalyst in the aqueous binder solution and to cure attemperatures above about 350 degrees F. to fully and quickly cure thebinder, providing hot wet strengths(soaked for 10 minutes in 180 degreeF. water) of 90-100 percent. To “B” stage these resins in the presentinvention, very little or even no cure catalyst need be used, but inthis case “B” stage cure temperatures of about 375 to 400 degrees isrequired. Preferably, up to about 10 weight percent, based on the weightof resin in the mat, most preferably about 5 to 10 weight percent, of acure catalyst like ammonium nitrate is used to speed “B” staging at arelatively low temperature. The mat is cured at temperatures betweenabout 300 and about 350 degrees F., such as 340 degrees F., for veryshort times, only 5-120 seconds, preferably 20-120 seconds. If the curetemperature is much less than 330 degrees F., the resultant mat will nothave adequate strength for handling and processing in the intended usesto avoid damage. If the cure temperature is much above 360 degrees F.the resin could cure too much and the mat will not bond as well to woodlater. Other catalysts can be used, such as organic aromatic acids likepara-toluene sulfonic acid and organic acids like maleic acid.

Processes for making nonwoven fiber glass mats are well known and someof them are described in U.S. Pat. Nos. 4,112,174, 4,681,802 and4,810,576, which references are hereby incorporated into this disclosureby reference, but any known method of making nonwoven mats can be used.The preferred technique for the making of mats of the present inventionis forming a dilute aqueous slurry of fibers and depositing the slurryonto an inclined moving screen forming wire to dewater the slurry andform a wet nonwoven fibrous mat, on machines like a Hydroformer™manufactured by Voith—Sulzer of Appleton, WS, or a Deltaformer™manufactured by Valmet/Sandy Hill of Glenns Falls, N.Y.

Next, the wet, unbound mat is transferred to a second moving screenrunning through a binder application saturating station where thefurfuryl alcohol formaldehyde resin based binder in aqueous solution isapplied to the mat. The excess binder is removed, and the wet mat istransferred to a moving oven belt where the unbonded, wet mat is driedand cured to only a “B” stage, bonding the fibers together in the mat.The partially cured mat is then usually wound into rolls and packaged.Mats made with the furfuryl alcohol formaldehyde resin binder can bestored without being protected from a humid atmosphere, but mats madewith phenolic resin or melamine formaldehyde resin binder should bestretch wrapped or shrunk wrapped or put into a plastic bag since thesebinders are hydroscopic and will take on moisture from a humidatmosphere.

The aqueous binder solution is preferably applied using a curtain coateror a dip and squeeze applicator. In the drying and curing oven the matis heated to temperatures of up to about 350 degrees F., but this canvary from about 210 degrees F. to as high as any temperature that willnot take the mat beyond “B” stage cure. The treatment time at thesetemperatures can be for periods usually not exceeding 1 or 2 minutes andfrequently less than 40 seconds. The lower the temperature selected forthe cure, the longer time required to reach “B” stage cure, but normallya temperature is selected that will reach “B” stage cure in no more thana few seconds, which is required on a commercial continuous glass matmanufacturing line.

EXAMPLE 1

A fiber slurry was prepared in a well known manner by adding 0.5 inchlong wet E type glass chopped fiber having fiber diameters averagingabout 10 microns to a known cationic white water containing Natrosol™thickening agent available from Hercules, Inc. and a cationic surfactantC-61, an ethoxylated tallow amine available from Cytec Industries, Inc.of Morristown, N.J., as a dispersing agent to form a fiber concentrationof about 0.8 weight percent. After allowing the slurry to agitate forabout 20 minutes to thoroughly disperse the fibers, the slurry wasmetered into a moving stream of the same whitewater to dilute the fiberconcentration to a concentration averaging about 0.05 to 0.06 weightpercent before pumping the diluted slurry to a headbox of a VoithHydroformer™ where a wet nonwoven mat was continuously formed.

The wet mat was removed from the forming wire and transferred to a SandyHill Curtain Coater where an aqueous UF binder (the Georgia Pacific UFdescribed above), modified with (mixed with) about 24 weight percent,based on the dry weight of the UF resin, of a blend of 91.7 weightpercent polyvinyl acetate homopolymer and 8.3 weight percent of anacrylic tripolymer, was applied in an amount to provide a binder levelin the cured mat of about 19-20 weight percent. The wet mat was thentransferred to an oven belt and carried through an oven to dry the matand to fully cure the modified UF resin to a temperature of about 450degrees F. The basis weight of the mat produced was 8.7 grams per squarefoot. The mat, containing 80-81 weight percent 10 micron E glass fiberand 19.5-21 percent modified urea formaldehyde binder, had the followingstrength properties:

Hot Wet Tensile (10 minutes in 180 degree 90+ percent F. water)Thickness 32-33 mils Loss On Ignition 19.5-21 weight percent MachineDirection Tensile 109 lbs./3 inches Cross Machine Direction Tensile 80lbs./3 inches Machine Direction Tear Strength 500 grams Cross MachineDir. Tear Strength 600 grams

6 inch by 6 inch layer of this mat was placed between two 6 inch by 6inch layers of softwood veneer, each having a thickness of about 0.10inch. This stack was put into a hot press subjected to a pressure ofabout 77 psi and a temperature of about 350 degrees F. for about 5minutes. After cooling the pressure was released and the stack was takenfrom the press. There was no bond between the wood layers and the matlayer.

EXAMPLE 2

Another mat was made in exactly the same way as in Example 1, exceptthat the average fiber diameter was 10 micron and the binder applied tothe wet nonwoven mat was an aqueous solution of FAREZ® X4P furfurylalcohol formaldehyde (FAF) resin binder and the wet mat was dried andthen heated to about 300-350 degrees F. for 1-2 minutes to “B” stage theresin binder. This finished mat contained 62.3 weight percent 0.75 inchlong, 13 micron E glass fiber and 37.7 percent “B” staged FAF resin andhad a basis weight of 1.7 lbs./100 square feet. the following physicalproperties:

Volatiles in the mat 6 weight percent (based on resin weight) Thickness27 mils Hot wet tensile 31 percent Loss On Ignition 37.7 weight percentMachine Direction Tensile 31 lbs./3 inch wide sample Cross MachineTensile 29 lbs./3 inch wide sample

The mat made in Examples 1 and 2 above were used to make a laminatedwood sandwich in the same manner as described in Example 1 except thatthe sandwich was subjected to 375 degrees F. for about 90 seconds at thesame pressure. The same test was repeated using one-eighth inchhardboard instead of the softwood veneer. In both cases, the mat ofExample 2 bonded the wood veneer and hardboard together tightly suchthat they could not be pulled apart by hand.

A layer of mat made according to this example was then placed on top ofone layer of the softwood veneer and a Teflon® separator sheet wasplaced on top of the mat before putting the sandwich into the press.This sandwich was pressed under the same conditions as above andremoved. When the separator sheet was removed (it didn't bond to themat) the mat was bonded tightly to the wood veneer and provided a toughsurface that would act to dimensionally stabilize the layer of wood andprotect the wood from physical abuse.

EXAMPLE 3

A mat was made as in Example 2, except that the basis weight wasincreased to 5.1 lbs./100 sq. ft. The mat properties were as follows:

Volatiles—5.3 wt. percent of resin in mat

Hot wet strength—23 percent

Thickness—29 mils

Machine Direction (MD) Tensile Strength—48 lbs./3 inches

Cross Machine (CMD) Tensile Strength—46 lbs./3 inches

Mat made in this example was tested in the same manner as the mat inExample 2 and the results were even better.

EXAMPLE 4

Mat was made exactly the same as in Example 1 except that the resin usedwas Georgia Pacific's 144D64 phenol formaldehyde (PF) and the mat wasdried and heated to 320 degrees F. for 5 minutes to “B” stage the PFresin binder. The finished mat contained 52.5 percent glass fiber and47.5 percent “B” staged PF resin, was very hydroscopic and had thefollowing properties:

Basis weight—3 lbs./l00 sq. ft.

Volatiles—4.3 percent of the resin

Thickness—35 mils

Hot wet tensile—0 percent

MD tensile—70 lbs./3 inches

CMD tensile—60 lbs./3 inches

This mat was tested in the same manner as described in Example 2 andproduced similar results as the “B” staged FAF resin bound mat.

This mat was also laminated to each face of a one eighth inch thickhardboard and to each side of a one half inch thick oriented strandboard using the laminating procedure described in Example 2. Sampleswere cut from these two laminates and from the unfaced hardboard andunfaced oriented strand board. All of these samples were then tested formodulus of rupture, flexural strength, with the well known three pointloading procedure. The results were as follows:

TABLE Sample Modulus of Rupture (psi) % Change Hardboard 80 0Mat/hardboard/mat laminate 114 +42.5 Oriented Strand Board (OSB) 125 0Mat/OSB/Mat 173 +38.4

The mat layers did not delaminate from either the hardboard or the OSBpreceding or during failure of the laminate, but instead broke with thehardboard and the OSB. This higher flex strength of the laminates meansthat laminate beams made with the mats of the present invention and inaccordance with the present invention can span greater lengths, supportgreater loads or both compared with laminates of the wood productsalone.

EXAMPLE 5

Mat was made exactly the same as in Example 1 except that the resin usedwas Borden's Astromel® CR-1 melamine formaldehyde (MF) resin describedearlier in the specification and the mat was dried and heated to 320degrees F. for 1-2 minutes to “B” stage the MF resin binder. Thefinished mat had the following properties:

Basis weight—2.3 lbs./100 sq. ft.

Thickness—26 mils

Hot wet strength—less than 10 percent

MD tensile—35 lbs./3 in.

CMD tensile—27 lbs./3 in.

This mat was tested in the same manner as described in Example 2 andshowed similar results.

While the preferred embodiments of the invention have been disclosed indetail, other embodiments within the described invention and havingother functional additives known or obvious to those skilled in the artare considered as part of the present invention and are intended to beincluded in the invention claimed below.

I claim:
 1. A laminate sandwich comprised of wood or a wood product in contact with a glass fiber nonwoven mat comprising glass fibers bonded together with about 15-75 weight percent of a resin binder wherein the resin binder is derived from an aqueous resin selected from a group consisting of furfuryl alcohol formaldehyde based resin, phenol formaldehyde resin and melamine formaldehyde resin and mixtures thereof, which resin is only partially cured to a “B” stage condition.
 2. The laminate as described in claim 1 wherein the major portion of the mat is glass fibers and up to 75 weight percent of the mat is fibers.
 3. The laminate as described in claim 1 wherein the mat also contains up to about 10 weight percent of a cure catalyst in the resin binder.
 4. The laminate as described in claim 1 wherein said glass fibers are less than 3 inches long and are in the form of a nonwoven mat.
 5. The laminate as described in claim 3 wherein said glass fibers are less than 3 inches long and are in the form of a nonwoven mat.
 6. The laminate of claim 1 wherein said mat also contains cellulosic fibers or fibers of a cellulosic derivative.
 7. A product produced by the method of pressing a wood or wood product against a fiber glass nonwoven mat while being heated to complete the cure of the binder in the mat, said mat comprising glass fibers bonded together with about 15-75 weight percent of a resin binder wherein the resin binder is derived from an aqueous resin selected from the group consisting of furfuryl alcohol formaldehyde based resin, phenol formaldehyde resin and melamine formaldehyde resin and is only partially cured to a “B” stage condition.
 8. A product as described in claim 7 wherein the major portion of the mat is glass fibers and up to 75 percent of the mat is fibers.
 9. A product as described in claim 8 wherein the mat also contains a cure catalyst in the resin binder.
 10. A product described in claim 7 wherein said glass fibers are less than 3 inches long are in the form a nonwoven mat.
 11. A product as described in claim 9 wherein said glass fibers are less than 3 inches long and are in the form of a nonwoven mat.
 12. A product as described in claim 7 wherein the resin binder in the mat contains up to 10 weight percent of a cure catalyst. 